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Has anyone else experienced this?

Tankerpilot75

Well Known Member
Finishing up my annual condition inspection and the A&P and I were checking connections and nuts on FWF. Everything was tight and secure except when we got to the fuel injector throttle body. Only one of the four nuts securing it to the engine was tight. Two were so loose you could spin them with your fingers and one was totally gone. The engine still ran smoothly.

Replaced all star lock washers, replaced the missing nut and tightened all to torque. We then added four nylon end nuts on top of the existing nuts and secured them - there was just enough room on the studs.

My A&P said this was the first time he?s ever seen nuts loosened like this - especially if no one?s worked on the item. He distinctly remembers checking the throttle body last year and every thing appeared secure then.

Our question: My engine is the Superior XP IO-360 B1AA2, has anyone else found they?ve had to tighten these nuts due to them becoming loose? This could have really ruined my day later this year if not discovered!
 
Jim
I have the same exact engine on my RV7. I have found mine tight at all times. I have never found them to be loose.

Stay safe & good luck.

Darren Kerns
RV7 N599DT
 
Nylon end nuts?

It's not a good idea to use AN364, AN365 nuts in hi temp environments (i.e. firewall forward). The "nylon" will degrade quickly and fail, allowing the nut to loosen, turn, fall off...
 
Nylon end nuts?

It's not a good idea to use AN364, AN365 nuts in hi temp environments (i.e. firewall forward). The "nylon" will degrade quickly and fail, allowing the nut to loosen, turn, fall off...

The A&P and I discussed this and felt like where these were located shouldn?t be a problem for the nuts, besides these are ?locking nuts? just helping to secure the primary nuts. Certainly better than no locking nuts at all given the recent discovery.
 
Finishing up my annual condition inspection and the A&P and I were checking connections and nuts on FWF. Everything was tight and secure except when we got to the fuel injector throttle body. Only one of the four nuts securing it to the engine was tight. Two were so loose you could spin them with your fingers and one was totally gone. The engine still ran smoothly.

Replaced all star lock washers, replaced the missing nut and tightened all to torque. We then added four nylon end nuts on top of the existing nuts and secured them - there was just enough room on the studs.

My A&P said this was the first time he?s ever seen nuts loosened like this - especially if no one?s worked on the item. He distinctly remembers checking the throttle body last year and every thing appeared secure then.

Our question: My engine is the Superior XP IO-360 B1AA2, has anyone else found they?ve had to tighten these nuts due to them becoming loose? This could have really ruined my day later this year if not discovered!

Nuts were not properly torqued, or something in the stack up ( servo/ brackets/ gaskets) was not right.
 
A quote from Vic S. on this exact topic.

"While doing a prebuy on Friday on an RV-8 I noticed a nut missing from the aft fuel servo mounting stud. This is not the first one of these I have discovered missing on an airplane. I know standard practice has been to use a nut, a lock washer, and washer, but for many years now I have been using AN363 all metal stop nuts with a washer in these locations and I have never seen one come loose. You might consider it on your airplane."

Here's the thread: http://www.vansairforce.com/community/showthread.php?t=148894&highlight=throttle+body+nuts
 
Yes indeed

Whilst I was completing my build another builder at our airfield had this same problem after 25hrs. Only one tight nut! The servo was about to fall off.
😳😳😳😳
I have added different types of metal locknuts. On top of the supplied ones.
one type is thin nut due lack of available threads.
Dont ask for part numbers as the docs are not handy.
 
Loose hardware.

Metal locknuts are not a bad idea. The probability of the correct hardware and gaskets coming loose after being properly torqued is incredibly small. I?ve seen a couple cases where the wrong gasket (thicker & softer) was installed and even though properly torqued, over a week or two would compress and unload the lock washers and allow whatever component to become loose. Extremely important that the mags have the right gaskets. My experience is that fuel servos are not unusually prone to coming loose. Always a great idea at every condition inspection or 100 hrs of operation to check the torque on every fastener you can reach.

Don Broussard A&P/IA/ATP
RV9 Rebuild in Progress
57 Pacer
 
Same setup on my RV7. No issues after 300 hours. I recommend torque seal here, to make verification easy.
Good luck and keep looking closely at everything...Jim
 
Look at certified aircraft and certified engines. They come from the factory with nylon lock nuts all over them. Look at the fuel injection line clamps. Look at the servo to sump or carb to sump attach nuts. While high-temp lock nuts (metal) are not a bad idea on small piston aircraft the heat resistant issue is not as important as in turbine installations. There are exceptions, of course. Like any lock nut close enough to exhaust manifolds or pipes or similar high-heat areas.

So take a look under the hood of a Cessna, Cirrus, Beech or Husky. Nylocks are the norm on these piston engines rather than the exception.

Jim
 
From AC 43-13

Hopefully you, as a builder, are familiar with FAA Advisory Circular AC-43-13B "Acceptable Methods, Techniques, and Practices Aircraft Inspection and Repair"

Specifically, 7-64, Paragraph f.

"Fiber or nylon self-locking nuts are not installed in areas where temperatures exceed 250 ?F."

That's all...


B
 
I have seen what you describe once.
Local RV driver had a new engine from a good shop that had inexplicably gone from running like a Swiss watch to running lean on two cylinders at higher power settings.
I was just doing a visual once over and when I got to the injector servo I saw a very small gap between the servo body and the intake. Can't recall now what the hardware was like (loose or missing) but once he re-secured the servo the engine went back to its old perfect self.

You could be OK running normal nylon locknuts but if it were me I would use a set of AN363.
 
I see I've been quoted already, but yes the use of metal nuts in this location should assure a tight, vibration-free conncetion.

It has been an acceptable practice to use plain nuts with lock washers for many years in this location. When star washers are used it is imperative that they are not re-used. They need to be replaced with new ones each time or they loose their locking ability. My guess is that this was a preferred method due to the chance that the fiber nuts could see temps higher than 250 degrees. While in theory they shouldn't see temps that high since they are attached directly to the sump in most, but not all cases (cold air induction as an example), there is a possiblity that after shutdown the temps in the RV lower cowls could get hotter for a while, being so tightly cowled. I have measured the bases of cylinders at 280 degrees after shutdown with a infrared thermometer.

The units are mounted to studs, so sometimes there has been some concern that using metal lock nuts could cause the studs to pull out when removing the metal lock nuts. I personally haven't seen that, but I haven't lived long enough to see everything yet. :)

The Jacobs engine on my Stearman has fiber nuts holding the carburator on it. Of course, temps may be a little cooler since it is out in the breeze.

Both the metal lock nuts and fiber nuts take a little more time to install and remove, but also offer some more protection for the same reason.

My preferred choices are nuts with new lockwashers or metal lock nuts. Check them every time the cowling is removed.

Vic
 
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